In machine tool operations, it is often necessary or desirable to provide a clamping chuck with automatic power clamping capabilities to insure adequate holding power for workpieces undergoing difficult and/or high speed machining. For example, power chucks having chuck jaws powered by hydraulic fluid or air pressure to provide clamping force for workpieces have been available in the industry from a variety of sources.
Some power chucks are designed for use on machines having hydraulic ports formed in the spindle nose, while others are provided as self-contained units complete with their own pressure gauge, pressure regulator, lubricator, filters, lines, fittings and the like. While such arrangements may be adequate in certain applications, (e.g., dedicated machines where the nature and size of the workpieces remain fairly constant, and interchange of the chuck devices themselves are infrequent), in situations where a machine tool is utilized for a variety of machining applications and/or the type, size, or other qualities of the workpieces vary rather frequently, power chucks requiring hydraulic or pneumatic pressure can create substantial obstacles to applicability, efficiency, manufacturing speed, and cost optimization. Such power chucks are also relatively complex, cumbersome, and expensive. All these factors add to the cost of obtaining, utilizing, and maintaining machine tools, and add to the costs of production of end products.
One common form of mechanical clamping device is the diaphragm chuck. Conventional diaphragm chucks generally include a plurality of clamping jaws affixed to a flexible diaphragm member. The jaws are normally spring-biased to either their "open" or "closed" position. A suitable actuator, such as a hydraulic or pneumatic cylinder is utilized to selectively axially flex the diaphragm in order to cause slight radial movement of the jaws to alternately firmly grip or release a workpiece on the chuck. Thus, these chucks are (a) normally closed and powered open; or (b) normally open and powered closed.
As with the power chuck arrangements, where workpieces of varying sizes or shape are to be chucked, a chuck having a different size diaphragm/jaw arrangement must normally be substituted. A diaphragm chuck of the normally closed and powered open type is shown in U.S. Pat. No. 2,462,501, which issued to G. Hohwart et al. The Hohwart et al. diaphragm chuck incorporates the use of hydraulic fluid to "spring" the diaphragm in order to release the jaw assemblies from gripping position, and relies upon the inherent spring action of the diaphragm to return the jaws to an original clamping position upon release of the hydraulic force.
U.S. Pat. No. 4,067,586, which issued to L. Morawski, illustrates a diaphragm chuck having a plurality of jaws fixed on a diaphragm to receive and cooperate with various workpiece clamping rings. In a manner similar to the Hohwart et al. diaphragm chuck, the Morawski chuck incorporates the use of pneumatic pressure to flex the diaphragm in order to release the workpiece from the jaws. When the air pressure is withdrawn, the Morawski device returns to its original clamping position. Clamping rings of different sizes can be substituted to accommodate various sizes of workpieces. As discussed above, however, the Morawski and Hohwart devices suffer from the inherent problems of complexity, cost, and cumbersomeness as a result of their requirement for pneumatic and/or hydraulic pressure lines to actuate their flexible diaphragms.
A workpiece holding chuck of the normally open and powered closed type utilizing pneumatic pressure to provide power assisted clamping force is shown in U.S. Pat. No. 2,582,680, which issued to A. Church. In the Church holding chuck, pneumatic pressure is utilized to inflate a bag structure which, in turn, flexes a diaphragm to tighten the normally open jaws onto the workpiece.
U.S. Pat. No. 2,824,744, which issued to J. Peters, illustrates a collet chuck wherein one or more bellows-like annular collets are compressed axially to provide clamping pressure in a radial direction. Particularly, the Peters flexible collet chuck arrangement is described as including a draw bolt which is threaded to a connector, which, in turn, is screw threaded for connection to a draw bar. The draw bar may further extend to a fluid pressure draw bar actuator at the opposite end of the spindle. Consequently, while this arrangement might be useful for gripping cylindrical shapes of relatively consistent size, it is not easily adaptable to conditions requiring relatively frequent and quick exchanges of clamping chucks, as is often required in modern machine tool operations.
Consequently, heretofore there has not been available a quickly interchangeable clamping chuck which remains passively clamped during chuck interchange procedures and is actively further clamped when the chuck is positioned at the machine work position. Moreover, there has not been available a relatively simple, reliable, exchangeable clamping chuck having the aforesaid combined passive and active clamping features, which can accommodate applications requiring mechanical power assist utilizing a draw bar assembly which remains at the machine work position.